Cationically electrodepositable coating composition

Abstract

The present invention provides a cationically electro-depositable coating composition comprising as a cross-linking agent, a blocked polyisocyanate having a blocked isocyanate group represented by Formula (I): (wherein R 1 represents a hydrogen atom, methyl, ethyl or propyl, and R 2 represents methyl or ethyl) or a self cross-linking type base resin having the blocked isocyanate group represented by Formula (I) described above.

What is claimed is:  
     
       1. A cationically electrodepositable coating composition comprising as a cross-linking agent, a blocked polyisocyanate having at least 0.1 blocked isocyanate group represented by Formula (I):                    
       wherein R 1  represents a hydrogen atom, methyl, ethyl or propyl, and R 2  represents methyl or ethyl. 
     
     
       2. The cationically electrodepositable coating composition as described in  claim 1 , wherein the blocked polyisocyanate is obtained by blocking at least one of isocyanate groups of a polyisocyanate compound with an amide compound represented by Formula (II): 
       
         
           R 1 —CO—NH—R 2   (II)  
         
       
       wherein R 1  and R 2  are synonymous with those defined in  claim 1 . 
     
     
       3. The cationically electrodepositable coating composition as described in  claim 2 , wherein the polyisocyanate compound is an aromatic diisocyanate. 
     
     
       4. The cationically electrodepositable coating composition as described in  claim 2 , wherein the amide compound is N-methylacetamide, N-ethylacetamide, N-methylpropionamide or N-methylformamide. 
     
     
       5. The cationically electrodepositable coating composition as described in  claim 1 , comprising an amine-added epoxy resin as a base resin. 
     
     
       6. The cationically electrodepositable coating composition as described in  claim 1 , further comprising a dialkyltin aromatic carboxylic acid salt as a cross-linking accelerating agent. 
     
     
       7. A cationically electrodepositable coating composition comprising as a base resin, an active hydrogen-containing cationic resin having at least 0.1 blocked isocyanate group per molecule on the average represented by Formula (I):                    
       wherein R 1  represents a hydrogen atom, methyl, ethyl or propyl, and R 2  represents methyl or ethyl. 
     
     
       8. The cationically electrodepositable coating composition as described in  claim 7 , wherein the base resin is a self (internal) cross-linking type cationic resin obtained by half-blocking an active hydrogen-containing cationic resin with an amide compound represented by Formula (II): 
       
         
           R 1 —CO—NH—R 2   (II)  
         
       
       wherein R 1  and R 2  synonymous with those defined in  claim 7 . 
     
     
       9. The cationically electrodepositable coating composition as described in  claim 8 , wherein the polyisocyanate compound is an aromatic diisocyanate. 
     
     
       10. The cationically electrodepositable coating composition as described in  claim 8 , wherein the amide compound is N-methylacetamide, N-ethylacetamide, N-methylpropionamide or N-methylformamide. 
     
     
       11. The cationically electrodepositable coating composition as described in  claim 8 , wherein the active hydrogen-containing cationic resin is an amine-added epoxy resin. 
     
     
       12. The cationically electrodepositable coating composition as described in  claim 7 , wherein the active hydrogen-containing cationic resin contains 0.2 to 2.0 blocked isocyanate groups per molecule on the average represented by Formula (I). 
     
     
       13. The cationically electrodepositable coating composition as described in  claim 7 , further comprising a dialkyltin aromatic carboxylic acid salt as a cross-linking accelerating agent. 
     
     
       14. The cationically electrodepositable coating composition as described in  claim 7 , further comprising as a rust preventive, a bismuth compound selected from the group consisting of inorganic bismuth compounds and organic acid bismuth salts. 
     
     
       15. A cationically electrodepositable bath comprising the cationically electrodepositable coating composition as described in  claim 1  or  7 . 
     
     
       16. A cationically electrodepositable coating method characterized by using the cationically electrodepositable coating composition as described in  claim 1  or  7 .